Concentrated photovoltaic and solar heating system

ABSTRACT

A solar power system concurrently generates electricity and a heated transparent fluid while maintaining the solar cells at an optimum temperature and optimizing the heat transfer by matching the refractive index of the secondary sunlight concentrator to the transparent fluid. A solar tracker aligns a primary sunlight concentrator to collect sunlight and directs the sunlight and a system for transferring solar heat to a transparent fluid and into a solar power electrical generating system. The concentrated sunlight transfers solar heat to a transparent fluid via first pass through the transparent fluid. The concentrated sunlight is further concentrated to raise its temperature by passing the concentrated sunlight through a secondary sunlight concentrator, and then passed again through the transparent fluid to transfer heat. The solar energy diminished concentrated sunlight strikes a solar cell array to generate electricity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/584,050 filed Aug. 27, 2009 titled CONCENTRATED PHOTOVOLTAIC ANDSOLAR HEATING SYSTEM, and is related to U.S. patent application Ser. No.12/584,052 titled “LOW NUMERICAL APERTURE (LOW-NA) SOLAR LIGHTINGSYSTEM,” filed Aug. 27, 2009 and is related to U.S. patent applicationSer. No. 12/584,051 titled “GENERATING ALTERNATING CURRENT FROMCONCENTRATED SUNLIGHT” filed Aug. 27, 2009 all of which are incorporatedby reference. These patent applications claim the benefit of priority ofU.S. Provisional Application No. 61/094,113 titled “One-axis trackingconcentrating photovoltaic and solar hot water hybrid system”, U.S.Provisional Application No. 61/094,115 titled “Alternating currentelectricity generation from concentrated sunlight”, U.S. ProvisionalApplication No. 61/094,120 titled “Solar lighting system with one-axistracking”, and U.S. Provisional Application No. 61/094,117 titled “LowNumerical Aperture (Low-NA) Solar Lighting System”, all filed Sep. 4,2008 and all of which are incorporated by reference.

BACKGROUND

1. Field of Invention

This invention relates to the field of solar energy and specifically forusing concentrated sunlight for the concurrent generation of electricitywithin the same system as heating of a fluid for heating applications.

2. Related Art

Typical solar energy systems generate electrical power by either thedirect conversion of concentrated or unconcentrated sunlight using solarcells (concentrated photovoltaic, CPV), or by using concentrated solarthermal (CST) energy to generate a pressurized vapor for turning aturbine-generator.

Concentrated photovoltaic (CPV) systems have a moderate efficiency ofabout 40% under a concentration of 500 suns and at an ambienttemperature of 25 degrees C. The solar cells are sensitive totemperature, however, so that the efficiency drops to about 35% at about100 degrees C., which highly concentrated sunlight is capable ofachieving as shown in the use of concentrated sunlight to boil water forevaporation systems. In addition, concentrated photovoltaic (CPV)systems need a two-axis solar tracking and are expensive. As such, thereturn of investment period for localized installations is many years.

Concentrated solar thermal (CST) energy systems, on the other hand, canand must operate at a high temperature, and may reach a thermalefficiency of 60-80%. Collector to grid energy conversion losses,however, lowers the overall efficiency to about 15%. In addition,turbine-generator systems have inherent safety issues and are highmaintenance, which raises the cost of the delivered power. As such,concentrated solar thermal (CST) energy systems are not suitable forlocalized installations.

SUMMARY OF THE INVENTION

Systems and methods provide for the solar generation of electricity andtransferring solar heat to a transparent fluid with a solar powergeneration system having a primary sunlight concentrator and a secondarysunlight concentrator with a refractive index matched to the refractiveindex of the transparent fluid and using the transparent fluid tomaintain the solar cell array at an optimum temperature.

A solar tracking system aligns the primary sunlight concentrator towardsthe sun for concentrating sunlight and directs the concentrated sunlightinto a solar power generating unit. The solar tracking system may be aone-axis azimuth tracking system or a two-axis system.

A transparent fluid is heated by passing concentrated sunlight throughthe transparent fluid, then further concentrating the sunlight andpassing the further concentrated sunlight through the transparent fluida second time. The transparent fluid also absorbs some the ultravioletlight that is harmful to some solar cells. The concentrated sunlightthen strikes a solar cell array to generate electricity, which generatesmore heat. The heat is removed from the solar cell by the transparentfluid. In some embodiments the transparent fluid may be pumped throughthe solar power generating unit. In some embodiments the transparentfluid may be in convection motion through the solar power generatingunit.

Different embodiments provide for using different concentrator systems.A concentrator system may have a parabolic trough primary concentratorwith a compound parabolic secondary sunlight concentrator. Aconcentrator system may have a Fresnel lens primary concentrator with acompound parabolic secondary sunlight concentrator.

The solar power generation unit may be within a single transparentcontainment system suspended above a second solar cell array forcapturing sunlight that misses the solar power generation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Elements in the figures are illustrated for simplicity and clarity andare not drawn to scale. The dimensions of some of the elements may beexaggerated relative to other elements to help improve the understandingof various embodiments of the invention.

FIG. 1 shows an embodiment of the concentrated photovoltaic and solarheating system the solar generation of electricity and a heated fluid.

FIG. 2 shows the internal components of the solar power generation unit.

FIG. 3 shows an embodiment of the at least one secondary sunlightconcentrator.

FIG. 4 shows an alternate embodiment of the concentrated photovoltaicand solar heating system for the solar generation of electricity and aheated fluid.

FIG. 5 shows another embodiment of the concentrated photovoltaic andsolar heating system.

FIG. 6 shows a flowchart of a method for the solar generation ofelectricity and a heated fluid.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment 100 of the concentrated photovoltaic andsolar heating system. The embodiment 100 may comprise a solar tracker105, a primary sunlight concentrator 110, concentrated sunlight 115, anda solar power generation unit 120.

The solar tracker 105 supports and orients the concentrated photovoltaicand solar heating system 100 towards the sun. The solar tracker 105 maybe one-axis azimuth tracking system, a dual-axis azimuth and elevationtracking system, or in some embodiments, the solar tracker 105 may be astationary system.

The primary sunlight concentrator 110 receives incoming sunlight. Insome embodiments, the primary sunlight concentrator 110 may be aparabolic trough. On receiving the sunlight, the primary sunlightconcentrator 110 concentrates the sunlight and redirects theconcentrated sunlight 115 to the solar power generation unit 120.

The solar power generation unit 120 comprises a transparent tube 125, anelectrical power port 130, a fluid inlet 135, a fluid outlet 140 and twosolar power generation systems. The transparent tube 125 houses the twosolar energy conversion systems while permitting the discharge ofelectrical energy via the electrical power port 130, and the ingress andegress of a transparent fluid (described in FIG. 2) via the fluid inlet135, and the fluid outlet 140 respectively.

The transparent tube 125 may be an optical clear glass tube or acrylictube. An anti-reflection (AR) coating or AR film may be applied to theouter surface of the transparent tube 125 to reduce the reflection loss.

FIG. 2 shows the internal components of the solar power generation unit120. The solar power generation unit 120 comprises at least onesecondary sunlight concentrator 205, a solar cell array 210, a solarcell frame 215, a cooling gap 220 and a transparent fluid 225.

On reaching the solar power generation unit 120, the concentratedsunlight 115 passes through the wall of the transparent tube 125 andinto the transparent fluid 225 within the transparent tube 125.

Flowing through the interior space of the transparent tube 125 is thetransparent fluid 225, which enters the solar power generation unit 120via the fluid inlet 135, and exits via the fluid outlet 140. In someembodiments, the transparent fluid 225 is in active motion through thetransparent tube 125 due to a pump (not shown). In some embodiments, thetransparent fluid 225 is in passive motion, i.e. via convection, throughthe transparent tube 125.

On passing through the transparent fluid 225, the concentrated sunlight115 loses some of its heat energy to the transparent fluid 225. Theconcentrated sunlight 115 then enters the at least one secondarysunlight concentrator 205. The at least one secondary sunlightconcentrator 205 further concentrates the solar energy of theconcentrated sunlight 115 to 300 to 500 suns. On passing through the atleast one secondary sunlight concentrator 205, the concentrated sunlight115 enters the cooling gap 220, which is filled with the flowingtransparent fluid 225. Due to the additional energy concentration of theat least one secondary sunlight concentrator 205, the concentratedsunlight 115 is again hotter than the transparent fluid 225, andtransfers this remaining heat to the transparent fluid 225. Theconcentrated sunlight 115 then enters the solar cell array 210 and isconverted to electrical energy by the solar cell array 210, which may beaffixed in an optimal location of the transparent tube 125 with respectto the at least one secondary sunlight concentrator 205 by the solarcell frame 215. The transparent fluid 225 removes the heat generated bythe concentrated sunlight striking the solar cell array 210 as well asthe heat generated by the electrical energy created by the solar cellarray 210.

As shown in FIG. 2, the transparent fluid 225 flows below, around andabove the at least one secondary sunlight concentrator 205 and is heatedby the concentrated sunlight 115 and by the solar cell array 210 beforeexiting the solar power generation unit 120 via the fluid outlet 140 toa heat exchanger system (not shown). The heat exchanger system uses orremoves the heat from the transparent fluid 225 for use in heating or inanother application. In some embodiments, a fresh supply of transparentfluid 225 is fed from a source to the solar power generation unit 120via fluid inlet 135. In some embodiments, the transparent fluid 225 isre-circulated to the solar power generation unit 120 via fluid inlet135.

An optimal total energy output of the solar power generation unit 120may be achieved by matching the at least one secondary sunlightconcentrator 205 to the transparent fluid 225 and to the solar cellarray 210. While multiple factors are considered, there is aninterdependence of these factors to reduce sunlight energy losses andyet achieve the best heat energy transfer and optimize electricaloutput.

FIG. 3 shows an embodiment 300 of the at least one secondary sunlightconcentrator 205. One factor of optimal total energy output of the solarpower generation unit 120 is that the energy level of the concentratedsunlight 115 is dependent on the configuration of the at least onesecondary sunlight concentrator 205. In some embodiments, the at leastone secondary sunlight concentrator 205 may be a compound parabolicconcentrator (CPC). To achieve optimal energy output in the one-axistracking system, the collecting angle (q sub in) of the secondarysunlight concentrator along line ‘A’ should be greater than 23.5degrees. This is due to the angle of incidence onto the normal of theCPC, which varies between +23.5 degrees at the summer solstice and −23.5degrees at the winter solstice. The collecting angle perpendicular toline ‘A’ should be greater than the maximum exit angle of the primarysunlight concentrator 110. To achieve a concentration ratio of 8 to 12,the exit angle (q sub out) of the CPC should be about 60 to 70 degrees.The concentration ratio for the primary sunlight concentrator 110 isabout 30 to 60. Together, the pair of the primary sunlight concentrator110 and the secondary sunlight concentrator 205 as described below willconcentrate the energy level of the incoming sunlight to about 500 timesthat of un-concentrated sunlight.

To further improve electrical output, the secondary sunlightconcentrator 205 may be designed to have a total-internal-reflection(TIR) in the transparent fluid 205. This may be achieved by having thesecondary sunlight concentrator 205 made hollow with a material having arefraction index smaller than the refraction index of the transparentfluid 225 with the transparent fluid 225 inside the secondary sunlightconcentrator 205. For example, the refractive index of transparentTeflon FEP is about 1.34 and the refraction index of Teflon AF 2000 isonly about 1.29. Thus, hollow transparent Teflon FEP or Teflon AF 2000may be used as the secondary sunlight concentrator with mineral oil,which has a refractive index of about 1.46

A total-internal-reflection (TIR) may also be achieved by having thesecondary sunlight concentrator 205 made solid with a material having arefraction index greater than the refraction index of the transparentfluid 225. For example, the refractive index of acrylic is about 1.49and the refractive index of Pyrex glass is about 1.47. Consequently,solid acrylic or Pyrex may be used with water, which has a refractiveindex of about 1.33.

Teflon products, however, are more expensive than other higherrefractive index materials. To lower the cost of the secondary sunlightconcentrator 205, transparent Teflon FEP or Teflon AF 2000 may beapplied as an internal coating to a hollow secondary sunlightconcentrator 205. In such a case, neither the total-internal-reflection(TIR) nor the reflective index of the secondary sunlight concentrator orthe transparent fluid needs to be considered.

Another factor is that the amount of heat energy absorbed from theconcentrated sunlight 115 and the heat generated by the solar cell array210 is dependent on the thermal conductivity and heat capacity, i.e. thematerial composition, of the transparent fluid 225. The thermalconductivity of water is 0.58 W/mK, while the thermal conductivity ofmineral oil is 0.138 W/mK, i.e. about ⅕ of that of water. Conversely,the heat capacity of water is 4.19 kJ/kgK, while the heat capacity ofmineral oil is 1.67 kJ/kg K.

Another factor is that the electrical output of the solar cell array 210may be temperature dependent. The temperature of the solar cell array isa function of ambient temperature around it, which in turn depends onthe flow rate of the transparent fluid 225, the solar heat of theconcentrated sunlight 115 striking the solar cell array 210 and the heatcreated by the generated electricity. The temperature of the flowingtransparent fluid 225 is proportional to the amount of concentratedsunlight 115 passing through the transparent fluid 225 and is inverselyproportional to the flow rate of the transparent fluid 225, i.e. thesolar heat absorbed by the transparent fluid 225 is transferred to theoutside. Thus, the flow rate of the transparent fluid 225 may be raisedor lowered to adjust the temperature of the solar cell array 210 foroptimum electrical generation.

FIG. 4 shows an alternate embodiment 400 of the concentratedphotovoltaic and solar heating system. The embodiment 400 may comprisethe solar tracker 105, an alternate primary sunlight concentrator 405,the concentrated sunlight 115, and the solar power generation unit 120.

The solar tracker 105 supports and orients the concentrated photovoltaicand solar heating system 400 towards the sun. The solar tracker 105 maybe one-axis azimuth tracking system, a dual-axis azimuth and elevationtracking system, or in some embodiments, the solar tracker 105 may be astationary system.

The concentrated photovoltaic and solar heating system 400 incorporatesa linear Fresnel lens as the alternate primary sunlight concentrator405. In addition, the solar power generation unit 120 is orientedtowards the sun, rather than receiving the concentrated sunlight 115 asreflected sunlight.

As shown in FIG. 4, the alternate primary sunlight concentrator 405,i.e. the linear Fresnel lens, is between the sun and the solar powergeneration unit 120. As such, the solar power generation unit 120 isrotated to receive the concentrated sunlight 115 from the primarysunlight concentrator 405, which is above it in FIG. 4, i.e. as thoughthe sun is overhead. In some embodiments, the solar power generationunit 120 and the alternate primary sunlight concentrator 405 may berotated towards one side, as for higher latitudes or when the sun is lowin the sky. This change in configuration may affect the design andassembly of a frame attachment (not shown) to the solar tracker 105, butthe function and operation of the solar tracker 105 and the solar powergeneration unit 120 are sufficiently the same as to not havedistinguishing technical differences.

FIG. 5 shows another embodiment 500 of the concentrated photovoltaic andsolar heating system. The embodiment 500 may comprise the solar tracker105, the alternate primary sunlight concentrator 405, the concentratedsunlight 115, the solar power generation unit 120, a reflective compoundparabolic enclosure 505, and a secondary solar cell array 510 inside thereflective compound parabolic enclosure 505 opposite the solar powergeneration unit 120 from the alternate primary sunlight concentrator405.

The solar tracker 105 supports and orients the concentrated photovoltaicand solar heating system 500 towards the sun. The solar tracker 105 maybe one-axis azimuth tracking system, a dual-axis azimuth and elevationtracking system, or in some embodiments, the solar tracker 105 may be astationary system.

As with the embodiment 400, sunlight enters the alternate primarysunlight concentrator 405 and is concentrated and directed towards thesolar power generation unit 120. On a cloudy day, however, a largeportion of the incoming sunlight may be scattered by the clouds, so thatthe alternate primary sunlight concentrator 405 cannot direct theconcentrated sunlight 115 towards the solar power generation unit 120.The reflective compound parabolic enclosure 505 redirects theconcentrated sunlight 115 for the generation of electricity by thesecondary solar cell array 510. Consequently, with two solar cellarrays, the concentrated photovoltaic and solar heating system 500 stillproduces electricity even on a cloudy day, as well as transferring itsheat to the transparent fluid 225.

FIG. 6 shows a flowchart of a method for the solar generation ofelectricity and a heated fluid.

At step 601, sunlight is received and concentrated a first time;

At step 610, the concentrated sunlight is passed though a transparentfluid and transfers solar energy to the transparent fluid;

At step 615, the sunlight is concentrated a second time by passing itthrough a compound parabolic concentrator;

At step 620, the concentrated sunlight is passed a second time thoughthe transparent fluid and transfers solar energy to the transparentfluid;

At step 625, the concentrated sunlight strikes a solar cell andgenerates electricity.

The embodiments discussed here are illustrative of the presentinvention. Elements in the figures are illustrated for simplicity andclarity and are not drawn to scale. Some elements may be exaggerated toimprove the understanding of various embodiments. The descriptions andillustrations, as well as the various modifications or adaptations ofthe methods and/or specific structures described are within the spiritand scope of the present invention. Hence, these descriptions anddrawings should not be considered in a limiting sense, as it isunderstood that the present invention is in no way limited to only theembodiments illustrated.

What is claimed is:
 1. A solar power generation system for concurrentlygenerating electricity and heating a transparent fluid with solarradiation comprising: a solar tracking system for aligning a primarysunlight concentrator, a fluid heating system and a solar powerelectrical generation system towards the sun; a primary sunlightconcentrator comprising a parabolic trough for concentrating sunlightand directing the concentrated sunlight towards the fluid heating systemand the solar power electrical generation system; a fluid heating systemfor solar heating of a transparent fluid comprising a fluid transporttube, a compound parabolic concentrator as a secondary sunlightconcentrator and a transparent fluid, the transparent fluid heated bypassing concentrated sunlight from the primary sunlight concentratorthrough the transparent fluid, then further concentrating the sunlightthrough the secondary sunlight concentrator and then passing the furtherconcentrated sunlight though the transparent fluid a second time, andfurther heating the transparent fluid with heat from a solar cell array;and a solar power electrical generating system for generatingelectricity comprising the compound parabolic concentrator as thesecondary sunlight concentrator and the solar cell array receiving thefurther concentrated sunlight from the compound parabolic concentratorfor generating electricity.
 2. The solar power generation system forconcurrently generating electricity and heating a transparent fluid withsolar radiation of claim 1 wherein the secondary sunlight concentratoris hollow and has a refraction index less than a refraction index of thetransparent fluid.
 3. The solar power generation system for concurrentlygenerating electricity and heating a transparent fluid with solarradiation of claim 1 wherein the secondary sunlight concentrator ishollow and has a highly reflective inner surface.
 4. The solar powergeneration system for concurrently generating electricity and heating atransparent fluid with solar radiation of claim 1 wherein the secondarysunlight concentrator is solid and has a refraction index greater than arefraction index of the transparent fluid.
 5. The solar power generationsystem for concurrently generating electricity and heating a transparentfluid with solar radiation of claim 1 wherein the transparent fluid ismineral oil.
 6. The solar power generation system for concurrentlygenerating electricity and heating a transparent fluid with solarradiation of claim 1 wherein the transparent fluid is water.
 7. Thesolar power generation system for concurrently generating electricityand heating a transparent fluid with solar radiation of claim 1 furthercomprising adjusting the flow rate of the transparent fluid to maintainthe temperature of the solar cell array at an optimum temperature forgenerating electricity.
 8. The solar power generation system forconcurrently generating electricity and heating a transparent fluid withsolar radiation of claim 1 wherein the solar tracking system is aone-axis azimuth tracking system.
 9. The solar power generation systemfor concurrently generating electricity and heating a transparent fluidwith solar radiation of claim 1 wherein the solar tracking system is atwo-axis azimuth and elevation tracking system.
 10. The solar powergeneration system for concurrently generating electricity and heating atransparent fluid with solar radiation of claim 1 wherein thetransparent fluid is convection driven through the solar powergeneration system.
 11. The solar power generation system forconcurrently generating electricity and heating a transparent fluid withsolar radiation of claim 1 wherein the concentrated sunlight is heatdiminished by cooling with the transparent fluid.